1. Technical Field
The present invention relates to a method of fabricating a semiconductor device, and more particularly, to a method of fabricating a metal oxide semiconductor (MOS) field effect transistor device.
2. Description of Related Art
Metal oxide semiconductor field effect transistor (MOSFET) is a basic structure widely applied to various semiconductor devices such as memory devices, image sensors, and display devices. To meet the demand of lighter, thinner, and smaller electronic devices, the size of CMOS is continuously shrunk. Accompanying the miniaturization, however, comes the short channel effect which reduces the threshold voltage of a MOS device. Note that “short channel effect” is a general term covering numerous leakage mechanisms such as, to name a few, junction leakage, sub-threshold leakage, gate oxide tunnelling, hot-carrier injection, gate-induced drain leakage, and punch-through leakage. To avoid the problem, techniques like forming lightly doped drains having ultra shallow junction and pocket implant (halo implant) have been proposed. However, pocket implant is an angled implant process, and as the device scale reduces to 90 nm or smaller, it is more and more difficult to form the pocket doped region with accurate position and adequate dose.